Control element for capacitive currents



y 1934- H. P. MILLER, JR 1,960,415

CONTROL ELEMENT FOR CAPACITIVE CURRENTS Filed March 11, 1932 3Sheets-Sheet 1 DIELECTRIC l CONSTANT A B C I l I L I I 1 L06 FREQ. P l II POWER FACTOR I I l T 5 s f, f r L06 FREQ. f

PRESSURE CONTROL 23 DEVICE TEMP.

CONTROL )8 DEVICE INVENTOR HERMAN POTTS MILLER JR.

ATTORNEY May 29, 1934. H. P. MILLER, JR

CONTROL ELEMENT FOR CAPACITIVE CURRENTS Filed March 11, 1932 3 Shets-Sheet 2 PRESSURE CONTROL TEMF? CONTROL 18 DEViCE FREQ.

FREQ.

FREQ. FIG. 5

l INVENTOR HERMAN POTTS MILLER JR.

F} 6. 4- ATTORNEY RESISTANCE DIELECTRIC CONSTANT POWER FACTOR May 29,1934. P, MlLLER' J 1,960,415

CONTROL ELEMENT FOR CAPACITIVE CURRENTS Filed March 11, 1952 3Sheets-Sheet 3 49/ LOAD TEMP.

CONTROL la DEVICE I80 lOb lac lad I88 l6? (lag TEMF. TEMP TEMF! TEMP.TEMP. TEMP. TEMP! CONT. CONT. CONT. CONT. CONT. CONT. CONT.

42m {9 M jz" r4a 42b 49 .a T P 55 K47 FIG. 7

(I80! lab I I8? ([69' TEMP. TEMP! TEMP. TEMP. CONT. CONT. CONT. CONT. HH II N {NW- 46 60 6| 6m @Elll ENE 56a LOAD FIG. 6

ATTORNEY Patented May 29, 1934 PATENT OFFIQE CONTROL ELEMENT FOR CAPACITIVE' CURRENTS Herman Potts Miller, Jr., East Orange, N. J.

Application March 11, 1932, Serial No. 598,233

23 Claims.

This invention relates to a method of and means for employing dielectricmediums to control electric currents and more particularly for employingdielectric mediums whose impedance characteristics are adjustable.

Distributed capacitance occurs in many elements of electrical systemsdue to the proximity of conductors with alternating potentials ofopposite polarities. The dielectrics in such capacitances are often ofsuch low loss as to offer little impedance to harmonic, parasitic, ortransient wave frequencies impressed on the conductors. This may giverise to abnormal voltages which endanger insulation in the system orcause interference to other electrical systems. Attempts have been madeto control the effects of such undes'red frequencies by the use ofabsorbing circuits, reactors, resistors, or electrostatic shields. Thesehave not been entirely effective and in some cases have resulted in theloss of power at the normal frequency as well as at the undesiredfrequencies. In the present invention there are associated with thedistributed capacitances dielectric mediums whose losses are low at thenormal frequency but may be high at the undesired frequencies and may beadjusted to desired values at these frequencies by methods describedhereinafter.

It is an object of this invention to employ the dielectric medium of acondenser for characterizing the impedance of an electrical system.

Another object of this invention is to provide a dielectric medium forthe electrostatic field of capacity forming elements which will causethe impedance between such elements to vary with the frequency of thefield in a manner which may be prearranged. 7

Another object of this invention is to vary the phase and amplitude ofcurrents at one or more frequencies in an electrical circuit by treatingthe dielectric medium of a condenser associated with that circuit.

A further object of this invention is to provide in an electrical systeman improved method of and means for attenuating the currents of one ormore frequencies and wave form without decreas'ng the efficiency of thesystem at other frequencies.

A still further object of this invention is to employ a condenser forcoupling two or more electrical circuits and to control thecharacteristics of such coupling through treatment of the dielectricmedium in the condenser.

The novel features that I consider characteristic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with additional objects and advantages thereof, willbest be understood from the following description of certain specificembodiments, when read in connection with the accompanying drawings inwhich like reference characters represent like elements and in which:

Fig. 1 shows curves illustrating the manner in which the properties ofdielectric mediums employed in this invention vary with the logarithm ofthe frequency.

Fig. 2 is a vertical section of a condenser employing the principles ofthis invention.

Fig. 3 is a vertical section illustrating a method for treating theelectrostatic field of an inductor, Fig. 4 represents diagrammaticallythe reactances and resistances of such an inductor, while Fig. 5 showsthe manner in which certain properties of this inductor vary with thefrequency.

Fig. 6 is a vertical section of a transformer employing the principlesof this invention in the distributed capacitances of its windings.

Fig. 7 shows diagrammatically a power transmission. system employing anumber of elements utilizing this invention, while Fig. 8 shows asimilar system in which the transmission conductors are in the form of asheathed cable.

In this invention use is made of a so-called polar dielectric whosedielectric constant increases with the frequency over one frequencyrange and decreases with the frequency over another. Such a dielectricis said to have normal dispersion when the dielectric constant increaseswith frequency and anomalous dispersion when it decreases withfrequency. Most dielectrics have marked normal dispersion but only thepolar dielectrics have been found to have both normal and anomalousdisperson. In polar dielectrics high values of dielectric loss and powerfactor are also obtained at or near a particular frequency called thecharacteristic frequency. These properties have been observed in polardielectrics including gases, such as ammonia and sulfur dioxide;liquids, such as water, alcohol, castor oil and glycerine; and solids,such as ice and rosin. Each medium has a characteristic frequency of itsown some of which are known in the art, the range of such frequenciesbeing approximately from zero to 5 X 10 cycles per second and possiblyhigher.

Fig. 1 shows the approximate manner in which the dielectric propertiesof a liquid having anomalous dispersion vary with the logarithm of thefrequency, curve a being the dielectric constant and curve b the powerfactor. In curve a for the range of normal dispersion the dielectricconstant rises from a value A at a low frequency ft to a value 13 at afrequency ii. In the range of anomalous dispersion it drops from thevalue B to a value C at a very high frequency I The power factor, curve13, starts with a low value at f0, rises to a peak value at a frequency12 and returns to a low value at M. The characteristic frequency f ishigher than either f1 or is and may be approximately determined by thefollowing equation:

where T is the absolute temperature, 7; is the coefficient of viscosity,and K is a constant depending on the size of the molecules in thedielectric used. The relative position of fc with reference to f1 and f2for a given medium remains the same when fc is changed so thatincreasing T or decreasing 1; will increase f1 and in as well as fe- Toobtain a desired power loss in a condenser at a given frequency adielectric medium may be selected whose value of f2 under normalconditions of temperature T and viscosity 1; is the same as the givenfrequency and whose power factor at f2 is higher than necessary toproduce the desired loss. Adjustment to the proper loss may then be madeby raising or lowering the temperature T. The temperature and viscosityare in many cases interdependent so that an increase in temperaturecauses a decrease in viscosity. For this reason when starting with f2 atthe given frequency a slight increase in temperature will shift Jz to amuch higher frequency and cause a very large decrease in the loss, whilea corresponding decrease in temperature will shift ]2 to only a slightlylower frequency and cause very little decrease in the loss. Referring tocurve a it is seen that these changes in loss will be accompanied bychanges in dielectric constant. Increasing the tempera ture willincrease the dielectric constant up to the value B and then decrease itto the value A. Decreasing the temperature will decrease the dielectricconstant to the value 0. It has been found that the effect of decreasingthe viscosity may be obtained without changing the temperature bydiluting the medium with a less viscous medium. If the diluting mediumalso has the properties of anomalous dispersion, two characteristicfrequencies will be obtained and hence a high power factor will occurover two different frequency bands. If the diluting medium does not havethese properties, its effect will be simply that of decreasing theviscosity. In many dielectrics benzene and carbon tetrachloride may beused for diluting purposes. In the case of gaseous dielectrics theviscosity may be changed by adjusting the gas pressure.

Fig. 2 shows a form of condenser which may be used to select or employdielectric mediums in accordance with the principles of this invention.In this drawing a metal container 8 of any suitable conducting material,such as iron or copper, has mounted on its top opening an insulatingplate 9 of suitable material and dielectric strength. The plate 9 isattached to the container 8 in a manner to maintain the desiredconditions of temperature and pressure within the container. Inside ofthe container 3 and suitably spaced with reference to its sides is ametal condenser plate 10 shaped in a manner to equalize theelectrostatic stress in a dielectric medium 11 placed between the plate10 and the container 8. The medium 11 may be a gas, a liquid, or a solidhaving the properties of anomalous dispersion as enumerated above; acombination of two or more substances having these properties; or acombination of one or more of such substances with one or moresubstances not having the properties of anomalous dispersion. The plate10 is supported by a suitable condueting rod 12 which may be fastened tothe insulating plate 9 and which has on its upper end a suitableconnection terminal 13. Another connection terminal 14 may be attachedto the container 8. Surrounding the container 8 and connected to it in amanner to form an enclosing jacket is another container 16 of metal,wood, or a suitable heat insulating material. The jacket betweencontainers 8 and 16 may be filled with a gaseous, liquid, or a solidmedium 1'7 capable of storing heat and maintaining the temperature ofthe dielectric medium 11 at the desired value. The temperature of themedium 17 may be maintained at the desired value by means of atemperature control device 18 acting through connecting tubes 19 and acirculating coil 20 in the well known manner. The control device 18 mayinclude any suitable refrigeration or heating system well known in theart with thermostatic control. The pressure of the dielectric medium 11may be maintained at any value, such as that required to obtain thedesired characteristic fre quency f0, through a connecting tube 22 bymeans of a pressure control device 23. This device 23 may be a vacuum orpressure pump with an auto matic pressure regulator.

It is to be understood that the principles of the condenser of Fig. 2may be applied to other forms of condensers, such as variable tuningcondensers,

multiple plate fixed condensers, and condensers formed by conductors inclose proximity to each other. A dielectric medium of power factor anddielectric constant to meet specified operating conditions at a giventemperature maybe selected for any such form of condenser in the manneroutlined above. I have found, for example, that a condenser containing acommercial grade of castor oil at a temperature of '70 degreesFahrenheit when inserted in the radio frequency circuit of an oscillatorwould not permit oscillations at 45 X 10 cycles per second. Diluting thecastor oil with carbon tetrachloride made oscillations possible due tothe shift of the frequency in to a higher value. With a solution of 90%castor oil and 10% carbon tetrachloride by weight oscillations wereobtained at this frequency and temperature. Raising the temperature ofthe mixture to 95 degrees Fahrenheit caused the power factor to decreaseby at least 3%.

Fig. 3 shows the manner in which the principles of this invention may beapplied to the distributed capacitance of an inductor consisting of aspiral winding 2'7 constructed in such a manner as to give the desiredinductance, resistance, and distributed capacitance. Surrounding thiswinding, or associated with it in a way to influence its electrostaticfield, is a dielectric medium 28 which may be similar to and have thesame properties as the dielectric medium 11 in Fig. 2. The medium 28 maybe enclosed in a container '29 of a suitable material, such as glass,quartz, or copper, and constructed in such a manner as to havenegligible effect on the electrostatic and magnetic fields of thewinding 27. An insulating plate 30 of suitable material and dielectricstrength may be attached to an opening in the container 29 in a mannerto maintain desired conditions of temperature and pressure within thecontainer. Surrounding the container 29 and attached to the plate 30 isa container 31 containing a medium 32, preferably a poor electricalconductor, such as water or Transil oil, which is capable of storingheat and maintaining the temperature of the medium 28 at the desiredvalue. The temperature of the medium 32 and the pressure of the medium28 may be maintained at desired values by control devices 18 and 23similar to those in Fig. 2.

Figs. 4 and 5 illustrate the effect of a dielectric medium havinganomalous dispersion on the effective resistance of an inductor, such aswinding 27 in Fig. 3. It is well known that the electricalcharacteristics of a winding of this type may be representeddiagrammatically as in Fig. 4 in which inductor 35 and resistor 36represent the inductance and resistance respectively of the winding, andcondenser 37 and resistor 38 the distributed capacitance and itsdielectric resistance. The effective resistance of this com bination toa potential applied across terminals 39 and 40 when the dielectricmedium is air will vary with the frequency approximately in the mannershown in curve a of Fig. 5. In this curve frequency fro represents theresonant frequency of the inductor 35 and the condenser 3'7. Suppose nowthat the winding is surrounded with a dielectric medium whose dielectricconstant and power factor vary in the manner shown in curves a and b ofFig. 1 and the corresponding curves 0 and d of Fig. 5. Due to thegreater dielectric constant of the medium, the condenser 37 will have ahigher capacitance and the resonant frequency of the winding will beshifted to a lower frequency in. The effective resistance of the incurve b of Fig. 5. It is seen that the resistance at frequency f11 isthe same for both curves a and b but that curve b has a broader peak anddoes not decrease as rapidly at the higher frequencies. This effect isdue mainly to the shapes of the dielectric constant and power factorcurves. It is only at frequencies between fm and f1o that curve a hashigher values than curve b. Considerable adjustment of resistance valuesover particular frequency ranges may be obtained by selection of thedielectric medium and the adjustment of its temperature. It is alsopossible to combine the effects of windings whose peak frequencies inhave widely different values.

A winding having the resistance characteristics of curve b in Fig. 5 maybe advantageously employed in a conductor carrying current at a very lowfrequency, such as 60 cycles per second. At this frequency its impedancewould be low, but at high frequencies both its resistance and reactancewould be high. If the reactance happened to be tuned out at certain highfrequencies by reactance of opposite sign in the conductor or itsterminal equipment, the resistance would still be high enough toattenuate voltages at these frequencies. Using a winding having aresistance curve as in a of Fig. 5, only frequencies in the neighborhoodof I10 would be attenuated. At other frequencies the resistance would below and the winding might resonate with the conductor and terminalequipment thus helping to increase the amplitude of undesired highfrequency voltages.

Fig. 6 shows the manner in which the principles illustrated in Figs. 4and 5 may be applied to the protection of the windings" of a transformer42. This transformer may be of a form well known in the art, such as theshell type employed on frequencies in the neighborhood of 60 cycles persecond, and consist of a steel core 43 on which are positioned a primarywinding 44 and a secondary winding 45. The core 43 rests on and is inelectrical contact with a steel shell 46. Connections from the windings44 and 45 may be made to transmission line conductors 47 and 48 and to asuitable load 49. Conductor 4'7 may be connected to the shell 46 througha suitable jumper 50. Instead of using a medium such as Transil oil forcooling the core 43 and windings 44 and 45, a dielectric medium 51having the properties of anomalous dispersion, as described hereinabove,may be employed. The temperature of the dielectric medium 51 may bemaintained at a desired value in the same manner as in Fig. 3 by acontainer 31, medium 32,

temperature control device 18 and connecting The effective distributedcapacitance tubes 19. from the high potential conductor 48 and thewinding 44 to the shell 46 may be represented schematically by acondenser 52.

The winding 44 of transformer 42 may be sub-- ject to the effect ofvoltages of high frequency and steep wave front impressed on theconductors 47 and 48 by methods enumerated hereinafter. These voltagesmay be high enough to damage the insulation on winding 44 or to inducesufficient voltage into the winding 45 to damage insulation in thatwinding and in the load 49. By the use of a dielectric medium 51 havingthe properties of anomalous dispersion, the capacitance of condenser 52is made large so that it effectively shunts the winding 44 andattenuates the high frequency voltages. This reduces the dangerousvoltages impressed on the windings 44 and 45 and the load 49 and thuseliminates possible short circuits and insulation breakdowns.

Referring now to Fig. 7 there is shown a complete system fortransmitting power from an alternating current generating source 55 to aload 49 and employing many embodiments of my in vention. The source 55and load 49 may be connected to the transmission line conductors 47 and48 through suitable switches 56a and 56b and transformers 42a and 42b ofthe type shown in Fig. 6. In the conductor 48 may be inserted chokecoils 57a, 57b, and 570 of the form shown in Fig. 3. Between theconductors 47 and 48 at points subject to undesired high voltages may bepositioned condensers 58a and 58b of the form shown in Fig. 2. Each ofthe elements employing the principles of this invention may be providedwith a suitable control such as a temperature control device 18a, 18b,18c, and 18g. Pressure control devices as shown in Figs. 2 and 3 havebeen omitted from Figs. '7- and 8 for the purpose of simplifying thedrawings. These elements may be adjusted to cooperate with each other inproviding the desired impedance characteristics in different parts ofthe system. While a single phase transmission system has been shown forpurposes of illustration, it is to be understood that these elements maybe similarly applied to polyphase systems.

It is well known in the art that in addition to the fundamental andharmonic voltages from the source 55 destructive voltages of highfrequency and steep wave front may be impressed on the system of Fig. 7by surges due to opening or closing of the switches 56a and 56b; bylightning strokes to the conductors 47 and 48 or objects associatedtherewith; by short circuiting arcs between lines 47 and 48 or betweenelements of opposite polarity in the system; or through coupling withadjacent transmission systems. Due to the flexibility provided inemploying the principles of this invention, the impedancecharacteristics of the system may be adjusted so as to effectivelyattenuate all such disturbances to a harmless point without affectingits operation at the desired frequencies. Since these disturbances aregenerally momentary in character and would cause little heating of thedielectrics, the operating temperatures of the elements may be constantenough to permit the elimination of the temperature control devices 18a,18b, 18c, and 18g.

Fig. 8 shows a similar transmission system in which a part of thetransmission conductors 4'7 and 48 are embedded in a dielectric mediumand surrounded by a metallic casing 61. The dielectric medium 60 mayhave the properties of anomalous dispersion and be selected in themanner described hereinabove to give the desired transmissioncharacteristics at the average oper ating temperature of the cable. Inthis way undesired voltages of high frequency and steep wave front maybe attenuated in the cable, the system thereby having an intrinsicdamping action.

In general the principles of my invention permit imparting to many formsof condensers a wide variety of impedance characteristics. Thesecharacteristics may be accurately adjusted for particu lar operatingfrequencies. They permit the adjustment of distributed capacitance in amanner that is not possible with ordinary condensers and if thisadjustment is made over wide enough limits the loss characteristics neednot be changed. They also permit the introduction of resistance intodistributed capacitance in a more effective and efficient manner than ispossible with ordinary resistors. Finally they provide reactanceelements of predetermined impedance characteristics which may beemployed in series with other elements for attenuation purposes or inparallel with other elements for by-pass or coupling purposes.

Many modifications of my improved control elements for capacitivecurrents will be apparent to those skilled in the art and my invention,therefore, is not to be restricted to the specific embodiments chosenfor purposes of illustration, but is to be limited only by the scope ofthe appended claims.

What I claim is:

1. In combination, a reactance element having a plurality of capacitanceforming surfaces integral therewith, means for generating and impressingalternating potentials of different frequencies on said element, adielectric medium having the properties of anomalous dispersionassociated with said surfaces, and means for corn trolling the impedanceof said element to the currents resulting from said potentials, saidmeans causing a change in the dielectric properties of said medium.

2. In combination, a transmission line, a reactance element therein, aplurality of capacitance forming surfaces integral with said element,and a plurality of dielectric mediums having the properties of anomalousdispersion associated with said surfaces, said mediums imparting aprearranged impedance characteristic to said element.

3. In combination, a transmission line, a reactance element in saidline, a dielectric medium associated with said element having theproperties of anomalous dispersion, means for influenc ing said mediumwith transmitted vibrations at a plurality of frequencies over saidline, and a source of heat vibrations at a definite frequency forimpressing on and influencing said medium, said source causing amplitudechanges in said first vibrations which are greater over a particularband of said frequencies than over other bands.

4. In combination, a transmission line, an inductive winding locatedtherein having distributed capacitance, and a dielectric medium havingthe properties of anomalous dispersion associated with said windingcausing a prearranged impedance characteristic in said winding.

5. In combination, a transmission line, an inductive winding locatedtherein having distributed capacitance, and a plurality of dielectricmediums at least one of which has the properties of anomalous dispersionassociated with said Winding, said mediums causing prearranged impedancecharacteristics in said winding.

6. In combination, a transmission system, an inductive winding thereinhaving distributed capacitance, a dielectric medium having theproperties of anomalous dispersion associated with said winding, andmeans cooperating with said medium for controlling the impedancecharacteristics of said winding.

7. In combination, a transmission system, an inductive Winding thereinhaving distributed capacitance, a dielectric medium having the properties of anomalous dispersion associated with said winding, and atemperature control device for changing the impedance characteristics ofsaid winding.

8. In combination, an inductive winding having distributed capacitance,means for impressing a plurality of alternating potentials of differentfrequencies on said winding, a dielectric medium having the propertiesof anomalous dispersion cooperating with said Winding for attenuatingthe currents resulting from said potentials of at least one of saidfrequencies, and means for controlling the pressure on said medium.

9. In an electrical system, a transmission line, a plurality ofreactance elements located therein employing dielectric mediums havingthe properties of anomalous dispersion, and means for causing saidmediums to provide a prearranged impedance characteristic for said line.

10. In a transmission system, an alternating current energy source, aload circuit for said source, a transmission circuit connecting saidsource with said load circuit, means for changing the frequency of atleast a portion of the energy from said source, and means forattenuating at least a portion of the currents resulting from saidenergy of changed frequency without changing the alternating currentsfrom said source, said attenuating means comprising reactance elementsemploying dielectric mediums having the properties of anomalousdispersion.

11. In combination, a source of alternating current, a load circuit, andan impedance element for coupling said source to said load circuit, saidelement employing a dielectric medium having the properties of anomalousdispersion.

12. In combination, a source of alternating current, a load circuit, animpedance element for coupling said source to said load circuit andemploying a dielectric medium having the properties of anomalousdispersion, and means for changing the dielectric properties of saidmedium, said change in dielectric properties causing a change in saidcoupling.

13. In combination, a transmission system, an inductive winding thereinhaving distributed capacitance, a plurality of dielectric mediums atleast one of which has the properties of anomalous dispersion associatedwith said winding, and means cooperating with said mediums forcontrolling the impedance characteristics of said winding.

14. In combination, a transmission system, an inductive Winding thereinhaving distributed capacitance, a dielectric medium having theproperties of anomalous dispersion associated with said winding, and apressure control device for changing the impedance characteristics ofsaid winding.

15. In combination, an inductive winding having distributed capacitance,means for impressing a plurality of alternating potentials of differentfrequencies on said winding, a dielectric medium having the propertiesof anomalous dispersion associated with said winding causing attenuationof the currents resulting from the potentials of at least one of saidfrequencies, and means cooperating with said medium for changing theattenuation of said currents.

16. In combination, an inductive Winding having distributed capacitance,means for impressing a plurality of alternating potentials of differentfrequencies on said winding, a dielectric medium having the propertiesof anomalous dispersion associated with said winding causing attenuationof the currents resulting from the potentials of at least one of saidfrequencies, and means comprising temperature control of said medium forchanging the attenuation of said currents.

17. In a transmission system, an alternating current energy source, aloadcircuit for saidsource, a transmission circuit connecting saidsource with said load circuit, means for changing the frequency of atleast a portion of the energy from said source, means comprisingreactance elements employing dielectric mediums having the properties ofanomalous dispersion for attenuating the alternating currents resultingfrom said energy of at least one of said changed frequencies to agreater degree than the alternating currents from said source, and meanscooperating with said mediums for changing the attenuation of at leastone of said alternating currents.

18. In combination, a source of alternating currents of a plurality offrequencies, circuits containing a plurality of paths for said currentsconnected to said source, a plurality of reactance ele ments located insaid paths, and a dielectric medium having the properties of anamolousdispersion associated with at least one of said elements for preventingsaid currents of at least one of said frequencies from traversing atleast one of said paths.

19. In combination, a source of alternating currents of a plurality offrequencies, circuits containing a plurality of paths for said currentsconnected to said source, inductance elements having distributedcapacitance located in at least one of said paths, and a dielectricmedium having the properties of anomalous dispersion associated with atleast one of said inductance elements for introducing appreciable lossesinto at least one of said paths for at least one of said frequencies.

20. In combination, a source of alternating currents of a plurality offrequencies, circuits containing a plurality of paths for said currentsconnected to said source, a plurality of reactance elements located insaid paths, a dielectric medium having the properties of anomalousdispersion associated with at least one of said elements for attenuatingcurrents of at least one of said frequencies, and means cooperating withsaid medium for controlling said attenuation in at least one of saidpaths.

21. In combination, interconnected circuits forming a plurality of pathsfor electrical currents of different frequencies, a plurality ofreactance elements located in said paths, and a dielectric medium havingthe properties of anomalous dispersion associated with at least one ofsaid elements for attenuating currents of at least one of saidfrequencies.

22. In combination, a source of alternating current, a load circuit, animpedance element for coupling said source to said load circuit andemploying a dielectric medium having the properties of anomalousdispersion, and means comprising temperature control of said medium forcausing a change in said coupling.

23. In combination, a source of alternating current, a load circuit, animpedance element for coupling said source to said load circuit andemploying a dielectric medium having the properties of anomalousdispersion, and means comprising pressure control of said medium forcausing a change in said coupling.

HERMAN POTTS MILLER, JR.

